magma series mantle Flashcards
reflects the isotopic signature of the primitive mabtle as it would evolve to the present w/o any subsequent fractionation of the radioactive elements extracted to form continental and oceanic crust
BSE Bulk Silicate Earth
high pb 206/ Pb 204 ration suggestive of a source with high au but it is not enriched in Rb low Sr87/Sr86 old enough >1 Ga to develop the observed isotopic ratios by radioactive decay over time
HIMU (High myu)
high He3 and He 4 mantle reservoir act as a mixing conponent and explain the spread of OIB data in the He Sr Nd Pb systems
PHEM primitive Helium Mantle
represents a restricted isotopic range tht is common in ocean volcanic rocks
PREMA (Prevalent Mantle)
a high He3/He4 component lying approx midway between DM and HIMU that representd actual source material (a true mantle reservoir) or the partial melting process in rising OIB diapirs wc sampla a mixed DM-HIMU source in very consistent proportions
FOZO Focal Zone
restricted intermediate isotopic value where the convergence of Pb Nd Sr isotopic data for MORB and OIBs approaches a high He3/ He4 reservoirs
Common Mantle
source of N type MORB
DM reservoir
less wnriched and may also represent a crustal componentn either ancient oceanic crust or pelagic sediment or they may possibly have been entiched by intra mantle processes stranded melts or metasomatizing fluids
EMI and HIMU reservoirs
contain non depleted BSE partially depleted PREMA and non degassed FOZO PURM and C
OIB
region along the immediate plate boundary eithin wc volcanism is concentrated is also assoc with very high heat flow indicating an elevated geothermal gradient
neovolcanic zone
locus of considerable earthquake activity
ridge axis
formed where hydrothermal fluids in excess of 350 C cool dramatically upob escaping from vents and precipitate a number of minerlas including barite silica and several valuable metal sulfides
spires chimneys
subduction rate of island arc
0.9-10.8 cm/yr
arc type crust range
from 12-36 km
averages about 36km
stable only if the melt contains >3 wt. % H2O excess of 0.1 to 0.2 Gpa
black hornblende
correspond to steey dipping 25-30 seents of yhe subducting slab
active volcanic zones
correspond to zegments with much dhallowet dips 10-15 degrees of a segmented Nazca plate
inactive volcanic zones
originates from the fluid fluxed and LIL enriched mantle wedge above the subducting and dehydrating Nazca plate jn the same manner
andean magmatism
extends for about 1000km and corresponds to the length of the juan de fuca plate system subducting obliquely beneath the north american plate
cascade magmatic arc
100-300km long by 10-25 km wife tectonic slices of mafic to silicic volcaniclastic clastic and chemical sediments some tectonic melanges
greenstone belts
alkali picrite
ankaramite
co2 rich and less potassic than group 2 kimberlite
group I kimberlite
h2o rich and has a mica rich matrix
group II kimberlite (orangeite)
also known alkali basalts lamprophyres alpine peridotites 1-1.4 g percton and occur only underlain by rocks older than 2.5 Ga
diamonds
